The present invention relates to an improved vertically retractable support assembly useful, for example, in the support and exact vertical positioning of an image receptor or x-ray source in a radiation therapy system. Such support assemblies are useful in the cancer therapy system described in U.S. Pat. No. 4,870,287 and in the methods and apparatus described in U.S. patent application Ser. No. 07/332,549 filed Mar. 31, 1989, both of which are assigned to the assignee of the present invention. The Loma Linda University Medical Center, and both of which are incorporated herein by this reference.
As described in the referenced patent application, prior to proton treatment, a patient is positioned on a patient support or pod and x-rays are taken showing the position of the patient in the pod. Such position information is used to ensure continued proper positioning of the patient during treatment. Also, it is important during subsequent treatment that the patient be located in exactly the same position in the support pod. Therefore, prior to subsequent treatment, the patient is again placed in the support pod and x-rays taken and compared with the previous x-rays to determine any differences in patient position. Any differences in patient position are eliminated prior to the subsequent treatment by moving the patient in the pod and again taking and comparing x-rays. In the taking of all such x-rays it is important that the x-ray source and image receptor be in the exact same relative position in order for the x-ray information to be meaningful in determining the correct positioning and repositioning of the patient.
Prior support assemblies for image receptors have been vertically retractable usually from a ceiling mount to control the vertical position of the receptor relative to the patient. Such assemblies have comprised vertically telescoping tubes, the innermost one of the tubes carrying the image receptor. The vertical telescoping movement of the tubes is controlled either by ball bearings riding in aligned outer and inner vertical channels in the telescoping tubes or by guide rollers bearing on guide rails positioned on the outside of the telescoping tubes. The telescoping tubes are connected to a counterweight mechanism which permits an operator to slowly extend and then retract the telescoping tubes to establish the vertical position of the image receptor. Such prior vertically retractable assemblies are very costly, do not possess adequate lateral stability and are difficult to precisely maneuver to exact predetermined stops.
Accordingly, there is a need for a simplified, relatively inexpensive, laterally stable, vertically retractable support assembly which is capable of being easily maneuvered and precisely controlled to bring the assembly to exact vertical stop positions. The present invention satisfies such needs.